Eat food that contains high carbohydrate and protein.

1. Do this http://www.maximuscle.sg/static/caloriecalculatorwin.html
2. Hit the grocery store, read food labels, buy

When I just started (2 months ago), my real food source are
My primary food source for carb
- white rice (brown rice is slightly expensive, but better) - lunch, dinner
- bread - 7pcs per day (breakfast, 11am, 5pm - pre workout)
- milo - 9am, 3pm when i feel im bored at work

My primary food source for protein
- oat
- chicken breast w/o skin - im not strict on this, eat when i feel i like it
- egg
- peanut butter - eat with bread
- milk - i replace milk with soya, slightly cheaper, 30% less protein than milk

3. Read stickies, read articles from bodybuilding.com

I prefer to take carb from real food than mass gainer as carb are easy to find and cheap, and invested my money on whey protein.
Mass gainer is simply has not much serving(roughly like 20servings per 5lbs tub) as compared to whey protein which has more.

My meals are simple and easy to adapt for newbie because I am a newbie too, I give myself some tolerance and space to eat dirty food once in awhile to keep myself motivated and not bored with clean food.